A fluid jet assisted ion projection printer, of the type utilized herein, is disclosed in commonly assigned U.S. Pat. No. 4,463,363 issued on July 31, 1984 in the name of Robert W. Gundlach and Richard L. Bergen, entitled "Fluid Jet Assisted Ion Projection Printing". In that printer, an imaging charge is placed upon a moving receptor sheet, such as paper, by means of a linear array of closely spaced minute air "nozzles". The charge, comprising ions of a single polarity (preferably positive), is generated in an ionization chamber by a high voltage corona discharge and is then transported to and through the "nozzles" where it is electrically controlled, within each "nozzle" structure, by an electrical potential applied to modulating electrodes therein. Selective control of the modulating electrodes in the array will enable spots of charge and absence of charge to be deposited on the receptor sheet for subsequent development.
The modulating electrodes may be incorporated in an inexpensive and compact integrated marking head array which also includes multiplexed driver circuitry and thin film transistor switching elements. Data potentials are selectively imposed upon the modulating electrodes. Such an arrangement is disclosed in commonly assigned U.S. Pat. No. 4,584,592 issued on Apr. 22, 1986 in the names of Hsing C. Tuan and Malcolm J. Thompson, entitled "Marking Head for Fluid Jet Assisted Ion Projection Imaging Systems".
An alternative driving circuit for the integrated marking head array is disclosed in co-pending a patent application Ser. No. 861,472, filed May 9, 1986 in the names of Hsing C. Tuan and Malcolm J. Thompson, and entitled "Improved Writing Head". As described therein, a latching circuit, including a switching element electrically connects the marking electrodes directly to a source of reference potential.
A fluid jet assisted ion projection copier is disclosed in commonly assigned patent application Ser. No. 784,293, filed Oct. 7, 1985 in the names of Hsing C. Tuan and Malcolm J. Thompson, and entitled "Ion Projection Copier". The marking head array incorporates modulating electrodes and photosensors which may either directly drive the electrodes or indirectly drive the electrodes through an amplification circuit. Two types of thin film sensors are disclosed. One, a gap-type exhibits a photoconductive gain of about 5, but has a characteristically slow response time. The other, a sandwich type, has a photoconductive gain of unity, but has a very fast photocurrent response time. An amplification circuit, requiring at least three sources of reference potential (high, low and ground) is disclosed therein for enabling practical use of the low gain sandwich type photosensor.
From the foregoing it can be seen that both a printer and a copier configuration have been individually contemplated for this ion projection marking process. However, rather than providing the user with a different machine to perform each of these functions, we suggest a single machine having a multifunction marking head array incorporating, on a page-wide substrate, an image sensor array, a modulation electrode array, function switching electronics and data input-output electronics. All of the elements may be implemented monolithically on the substrate, preferably in thin film amorphous silicon and materials compatible with its processing.
In the PRINT mode of a multifunction machine, the operation would be as described in the aforesaid U.S. Pat. No. 4,584,592 and the image sensor array would not be operational. In the COPY mode, the image sensor array would generate a photo-induced current in response to light reflected from an illuminated document, and the photo-induced current would, in turn, drive the modulating electrodes to produce a copy of the document. In the SCAN mode, the image sensor array again would generate a photo-induced current in response to light reflected from an illuminated document, and the photo-induced current would be detected and amplified by data input-output electronics for either storage or transmission to a remote site.
The function switching electronics of the multifunction marking head array serves to set the machine's mode of operation. It may: (1) make operational either the image sensor array connections to the modulation electrode array and disable the data input-output electronics connections, for operating in the COPY mode; (2) make operational the image sensor array connections to the modulation electrode array and enable the data input-output electronics connections, for operating in the SCAN mode; or (3) disable the image sensor array connections to the modulation electrode array and enable the data input-output electronics connections, for operating in the PRINT mode.
It is the primary object of the present invention to provide a multifunction head array which will allow PRINT, COPY and SCAN functions to be selectively implemented and in which an amplification circuit on the array enables the COPY function to have a rapid, self biasing, linear response. It is a further object of this invention also to provide the amplification circuit for the SCAN function.
It is further object of a form of this invention to provide an amplification circuit on the array which will enable the COPY and SCAN functions to have a rapid, self-biasing, linear response.